Field of the Invention
The present invention relates to a method for producing a Group III nitride semiconductor through a flux method. More specifically, the method is characterized by a crucible for holding a melt. The present invention also relates to a crucible used when growing the Group III nitride semiconductor through the flux method.
Background Art
The so-called Na flux method is well known as a method for growing a GaN crystal. This method is a technique that can grow GaN at a relatively low pressure of a few MPa and a low temperature of 600° C. to 1,000° C. by introducing nitrogen gas in a molten mixture of Na (sodium) and Ga (gallium).
Japanese Patent Application Laid-Open (kokai) No. 2011-136898 and WO 2010/079655 disclose that in the Na flux method, a crucible for holding a melt and a seed crystal is made of ceramics such as alumina, yttria, and YAG (yttrium-aluminum-garnet).
Japanese Patent Application Laid-Open (kokai) No. 2011-136898 describes that the average grain size of the crucible may preferably be 1 μm to 100 μm on the viewpoint of anti-corrosion property against a flux. Similarly, on the viewpoint, the grain size of the powdery raw material may preferably be 0.1 μm to 10 μm.
WO 2010/079655 describes that alumina or silica is eluted from the crucible made of alumina.
In the growth of GaN through the Na flux method, crystal growth called “macro step growth” which forms a large step of a few μm to a few hundred μm order is observed. In a region of this macro step growth, the amount of melt (such as Na) incorporated into the crystal is increased, resulting in the deterioration of crystal quality.
However, the macro step growth could not be suppressed because the control factor of the macro step growth was unknown.